1. Field of the Invention
This invention relates generally to electrochemical cells utilizing a reactive metal anode and, more particularly, this invention relates to an electrochemical cell utilizing an alkali metal anode and to means for safely passivating such a cell.
2. Description of the Prior Art
Electrochemical cells utilizing a reactive metal anode (typically of an alkali metal such as lithium, for example), a cathode spaced from the anode to define a reaction space, and an aqueous alkaline electrolyte are well known. Many such cells utilize a silver oxide cathode, or a gas consuming cathode, such as an air cathode.
Such cells are described in detail in numerous patents and publications, including U.S. Pat. Nos. 3,791,871 (Rowley), 3,976,509 (Tsai et al), and 4,007,057 (Littauer et al), the respective disclosures of which are incorporated herein by reference.
Such cells are intrinsicly energetic, and therefore potentially explosive. Many prior attempts have been made to provide practical means for controlling the energy characteristics of such cells. One important objective of such research has been to provide means for safely and reliably shutting down or controllably passivating an operating electrochemical cell of this type.
Electrochemical cells of the reactive metal type generally utilize an aqueous alkaline electrolyte with which both the cathode and the anode are in contact during operation. Typically, the cathode and anode are at least partially immersed in the electrolyte during operation. In a typical lithium cell, the electrolyte comprises a solution of lithium hydroxide in water, which may be seawater. Often, the lithium hydroxide concentration in the electrolyte is controlled by circulating makeup water and electrolyte through a loop which includes the cell reaction spaces defined between cathode and anode pairs.
Prior attempts to shut down or control the electrochemical reaction rate have utilized ethylene glycol (a primary diol) as a shutdown fluid. However, ethylene glycol has a tendency to rapidly and violently react with the lithium anode or silver oxide cathode, which may cause an explosion.